Multiplex antenna distribution system



Sept. 23, 1952 E. LACEY 2,611,895

' MULTIPLEX ANTENNA DISTRIBUTION SYSTEM Filed Dec. 8, 1948 t wa f- 5 u vv 2 4 JNVENTOR.

By EDWARD LACE) ATTORNEY Patented Sept. 23, 1952 Ema UNITED STATESPATENT OFFICE MULTIPLEX ANTENNA DISTRIBUTION SYSTE (Granted under theact of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 19Claims.

This invention relates to multiplex circuits, and more specifically tomultiplex receiving circuits wherein a plurality of communicationchannels may be maintained over a common transmission means, such as anantenna, the several channeled signals being separated at the receivingend by a plurality of tuned circuits, each resonant to the particularsignal which it is desired that it extract from the antenna.

It is an object of this invention to provide an improved multiplexcircuit in which each of the individual channels presents a relativelyhigh impedance to the common transmission means. except when tuned toresonance, under which condition it presents an impedance matching thatof the transmission means, whereby optimum energy transfer may beeffected. Off resonance, the high impedance prevents an undesirabledrain of energy from the common transmission means.

It is another object of this invention to provide a multiplex circuit inwhich each individual resonant circuit has a very high Q.

In the design of multiplex circuits, either for receiving ortransmitting, it is desired to have optimum energy transfer, atresonance, between the transmission means, such as the antenna, and theindividual resonant circuit. This is achieved by matching the impedanceof each individual circuit at resonance to the impedance of the antenna.It is also desirable that the impedance presented to the transmissionmeans by each circuit when tuned ofi the resonant frequency, be quitehigh, in order that the particular circuit not drain energy from theantenna except when tuned to its own particular frequency. Briefly, itis desirable that a plot of impedance vs. frequency for each of theseveral multiplex circuits look somewhat like a V, the impedance aboveand below resonance bein quite high, and dipping at resonance to theimpedance value which is the conjugate of the impedance of thetransmission means and the circuit. at which point the transfer ofenergy will be maximum, by virtue of the impedance match.

It is also desirable in multiplex circuits, in fact in many tunedcircuits, that the energy loss in the circuit be kept to a minimum; thatis to say, the circuit should have a high Q, or a high ratio: wL/R.

Prior art multiplex circuits have achieved each of these desiderata, butalways at the expense of the other.

It is an object of the instant invention to achieve both these desirablefeatures simultaneously in a multiplex system,

It is another object to minimize cross-coupling between the severalmultiplexed circuits of the system.

It is a further object of the instant invention to provide a multiplexsystem which is broadband in its overall characteristics; wherein eachindividual circuit will present, at resonance, an optimum impedancematch to the common transmission means to which each circuit is coupled;and wherein each individual circuit will have a high Q.

It is a still further object to attain the above outlined desideratawithout the use of vacuum tubes with their consequent vulnerability tooverloading.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following description.

The multiplex circuit of the instant invention comprises a transmissionmeans to which each of the several multiplex circuits is coupled in somesuitable fashion. For purposes of example and to simplify thedisclosure, the multiplex circuit will be shown as a receiving circuit.although it is to be understood that the teachings of the instantinvention are equally applicable to a transmitting circuit. Furthermore,the transmission means common to the several individual circuits will beshown as a fixed impedance, broad-band antenna, although it is to beunderstood that the teachings of the instant invention are equallyapplicable to other types of transmission means, such as a cableextending between a transmitting and receiving station of a multiplextransmission system.

In accordance with the instant invention. broad-band transformer meansare coupled to the broad-band antenna. By the term broadband antenna orbroad-band transformer means" is meant a means in which the impedance,or impedance ratio, respectively, is substantially constant over a widefrequency range, so that within that range the reaction of theparticular means is the same to all frequencies.

The essence of the instant invention is the combination. with thetransformer means de-- scribed above, of a plurality of series-resonantcircuits connected to the other side of the transformer means. As ageneral rule, the impedance of the antenna and of the transmission lineto which it is connected is not very low, being in the order of perhaps50 ohms, which figure will be used hereinafter as exemplary of thetransmission means impedance. The impedance of a series-resonantcircuit, properly constructed, is

at resonance quite low, being in the order of 1 ohm, which figure willbe employed hereinafter as exemplary of the impedance of eachseries-resonant circuit at resonance. The essence of the instantinvention, therefore, is the use of step-down, broad-band transformermeans coupling the 50 ohm impedance of the antenna to the 1 ohm resonantimpedance of each seriesresonant circuit. The high turns terminals, thatis, the terminals on the 50 ohm side of the transformer, are connectedto the antenna. The several multiplexed series-resonant circuits areconnected to the low turns terminals of the transformer means, that is,the terminals on the low impedance side of the transformer. For theexemplary figures given above, the transformer means would be one havingan impedance ratio of 50 to 1 (a turns ratio of about '7 to 1).

Each of the generally similar multiplexed channels, which are fed withenergy from the common antenna, includes, in addition to itsseries-resonant circuit (which is preferably made tunable), a signalamplifying means associated with or connected to a portion, 1. e. one ofthe elements, of the series-resonant circuit. In the case of a receivingsystem, the amplifying means consists of suitable means for deriving asignal from the series-resonant circuit, and applying it to a suitablereceiver. In the case of a transmitting system, the amplifying meansconsists of a suitable means for applying a signal of predeterminedfrequency to the series-resonant circuit, which would, in turn, apply itto the antenna through the transformer means above discussed.

The impedance of each of the several seriesresonant circuits, atresonance, after reflection through the transformer means, issubstantially matched to the impedance of the antenna. For the exemplaryfigures used above, the impedance of the series-resonant circuit,connected to the low turns side of the transmission means, being 1 ohm,is, after reflection thru the transformer, approximately 50 ohms, thisbeing the impedance of the antenna itself. Thus at resonance, optimumimpedance match is obtained between the antenna and the particularchannel to which the incoming energy is fed. In welldesigned circuits,the impedance of the antenna is substantially resistive, and of course,the impedance of a series-resonant circuit at resonance is alsosubstantially resistive, so that it will be understood that matching ofimpedances referred to herein neglects reactive components, because ingeneral they are not to be found in circuits of the present sort. It isto be understood, however, that where the antenna, or (more generally)the transmission means, includes a reactive component, it may still bematched to each circuit of the multiplex system by simply including thecomplement of the antenna reactance in the individual circuit, inaccordance with known impedance matching teachings.

There will be described as examples of the instant invention, two majorspecies, each of these species having certain minor modifications whichmight be desired for some applications. These embodiments of the instantinvention will now be described in connection with the accompanyingdrawing, wherein:

Fig. 1 illustrates the first species of the instant invention, and ischaracterized by the use of a plurality of individual step-downtransformers, as the broad-band transformer means, which is one of theessential features of the instant invention;

Fig. 1A illustrates certain minor modifications that are suitable forthe circuit of Fig. 1 for particular applications;

Fig. 2 illustrates the second principal species of the instantinvention, wherein the broad-band transformer means constitutes asingle, stepdown transformer, to the low turns side of which isconnected a low impedance transmission line which feeds the severaltunable series-resonant circuits included in the several multiplexchannels of the complete system;

Fig. 2A illustrates how the circuit of Fig. 2 may bedmodifled slightlyfor particular applications; an

Figs. 3 and 4 are included to illustrate the disadvantages of attemptingto achieve a satisfactory multiplex system without the use of thebroad-band, step-down transformer means constituting one of theessential features of the instant invention.

Referring to Fig. 1, a transmission means H is shown, to which isconnected transformer means l2, feeding a plurality of generally similarmultiplex channels l3, l4, and It. For exemplary purposes, thetransmission means has been shown as an antenna I], which in the instantembodiment is broad-band and of fixed impedance, connected to atransmission line l8. For exemplary purposes, it will be assumed thatthe fixed impedance of the antenna l1 and of the transmission line I8 is50 ohms.

In the species of Fig. l, the transformer means l2 assumes the form of aplurality (in this case, three), of step-down, broad-band, powdered-ironcore, transformers l9, 2l, and 22, each having a turns ratio of /50 tol. The high turns terminals of the transformer means l2 are connected,as shown, to the transmission line l8.

The multiplex channel It, which is typical of the channels l3, l4, andI6, consists of a seriesresonant circuit 23, connected to the low turns,or 1 ohm, terminals of the transformer IS. The series-resonant circuit23 comprises an inductor 24, connected in series with a capacitor 26,the two in turn being connected to the secondary, or low turns, winding21 of the transformer IS. The series-resonant circuit 23 makes nosubstantial use of the transformer I! for tuning; the transformer servesonly as an impedance matcher.

In the example of Fig. l, a receiving circuit is shown. Therefore, radiofrequency energy appearing across the capacitor 26 is applied betweengrid and cathode of a tube 28, which represents the first stage of asuitable receiver amplifier. The capacitor 26 is shown as variable, oradjustable, so that the channel [3 may be tuned to any desired frequencyof the band which the receiving system of Fig. 1 is adapted to receive.The channels I and I8 are generally similar to the channel l3 describedabove.

The operation of the circuit of Fig. 1 will now be briefly considered.

Assume that the antenna I! is receiving energy of three differentfrequencies, Fl, F2, and F3. Channel l3, i. e. the series-resonantcircuit 23. is tuned to Fl; channel I is tuned to F2; and channel I6 istuned to F3. The impedance of the series-resonant circuit 23, at theresonant frequency Fl, will be very low, approximately 1 ohm. Reflectedthrough the transformer means l2, i.-e. its transformer l9, this 1 ohmimpedance appears on the transmission line I! and antenna l! as a 50 ohmimpedance, exactly matching that of the antenna l1 and line It.Therefore, for energy of frequency Fl there is optimum coupling and 5maximum transfer of energy from the antenna II to the channel l3.

To all frequencies other than Fl, channel l3, after reflection throughthe transformer means l2, presents a very high impedance, so that littleenergy is diverted into the channel l3, except at frequency Fl. Thedegree to which frequencies other than Fl are rejected by channel l3 isdependent directly on the character of the frequency response curve ofthe series-resonant circuit 23, which, in turn, depends directly uponthe Q of the circuit. Assuming, purely for example, thatthe inductor 24has an inductance of about 32 microhenries and that Fl is 1 megacycle,the Q of the series-resonant circuit 23 is equal to:

The term in the numerator is wL;" the term in the denominator is-thetotal resistance of the circuit, which is the 1 ohm impedance atresonance (pure resistance) of the series-resonant circuit 23, plus the1 ohm impedance of the low turns winding 21 of the step-down transformerIS: a total of 2 ohms. Carrying forth the above calculations yields avalue of 100 for the Q of the resonant circuit feeding the amplifyingtube 28. This is a relatively high value, and results in excellentdiscrimination by the channel l3 against all frequencies except Fl, towhich it presents, as outlined above, the 50 ohms required to obtainmaximum energy transfer from the antenna H.

The channels I and I6 react to the frequencies F2 and F3 respectively,in a similar manner. It is, therefore, seen that the single antenna l!is able to feed a large number of individual channels, each tuned to itsown frequency, with each channel having little or no effect on receptionby the other channels and taking energy from the antenna only at its owntuned frequency.

It has been found as a practical matter that it is often desirable toemploy, as the transformer means l2, suitable auto-transformer means inplace of the regular transformer exemplified at IS in Fig. 1. In thisevent, the circuit of Fig. 1 may be modified as shown in Fig. 1A,wherein the auto-transformer I9 is connected with its high turnsterminals to the antenna H, the tapped capacitor 26' of which isconnected in the usual manner across the grid-cathode of the amplifyingtube 28'.

While theoretically the transformer l9, or l9, as the case may be,reflects 50 ohms into the primary for every ohm in the secondary, thereis as a practical matter a tiny amount of flux leakage which results ina small inductive reactance in the transformer. This may be corrected asshown in Fig. LA by the insertion of a small adjustable capacitor 3|, inseries with the high turns windings of the transformer l9. It is to beunderstood that if desired this reactance-correcting capacitor may alsobe used with the regular transformer illustrated at l9 in Fig. 1.

A second principal species of the instant invention is illustrated inFig. 2, wherein l'la represents the broad-band antenna having a fixedimpedance of 50 ohms, for example. In this species, the step-downtransformer means assumes the form of a single, powdered-iron core,radio frequency transformer 33, having a 0' to 1 turns ratio. The highturns, or 50 ohms, side of the transformer 33 is connected betweenground and the antenna l'la. To the low turns winding 6 34 of thetransformer 33 is connected 9. 1 ohm transmission line 38, to which areconnected the several multiplexed channels l3a, a, and Ida.

Exemplary of the channels is the channel l3a, which comprises aseries-resonant circuit 23a, consisting of the inductor 24a and thecapacitor 26a, connected in series across the 1 ohm transmission line36.

Operation of the Fig. 2 species of the instant invention, as a receivingcircuit, will now be briefly considered. Assume that three frequencies,Fl, F2, and F3 are being received by the antenna lla. By means of theadjustable or variable capacitor 26a the channel l3a is tuned to Fl.Thus, at frequency Fl, 9. 1 ohm impedance is applied across the 1 ohmtransmission line 36, and to the low turns winding 34 of the transformer33. This 1 ohm impedance is reflected through the transformer 33 at a 50to 1 ratio, and appears on the high turns winding of the transformer 33as a 50 ohm impedance. This impedance matches that of the antenna Ho,and of the associated transmission line 31. so that at Fl there isoptimum transfer of energy from the antenna l'la to the channel l3a.Frequencies other than Fl are rejected by the series-resonant circuit23a, because at all other frequencies its impedance is much higher than1 ohm. Therefore, little or no energy other than that of Fl will bedrawn into the channel l3a. As in the first species, described in Fig.1, the effectiveness of unwanted frequency rejection depends upon the Qof the circuit, which includes the capacitor 26a, the inductor 24a, andthe low turns winding 34. The latter having an impedance ofapproximately 1 ohm, reflected from the 50 ohm antenna l'la through thetransformer 33, and the resonant circuit 23a having an impedance of 1ohm, the total impedance (which is essentially resistive) is 2 ohms. -Asin the first example, the wL of the circuit is approximately 200, sothat the Q of the circuit is in the order of 100, which is a very highQ, and which results in a sharp resonance curve and attendant excellentrejection of all frequencies except Fl.

In a similar manner, the channels Ila and lie reject all frequenciesexcept F2 and F3, respectively, to which they are responsive,respectively, with an impedance of 1 ohm, reflected through thetransformer means l2a as a 50 ohm impedance, matching that of theantenna lla.

It will be readily apparent that the transformer means l2 of Fig. 1 andthe transformer means l2a of Fig. 2 are substantially equivalent, theformer case using a 50 ohm line l8 to feed a plurality of 50 to 1impedance ratio transformers, the latter using a 50 to 1 transformer 33to feed a 1 ohm line 36, which in turn feeds the several channels of thesystem.

The circuit of Fig. 2 has the practical advantage of requiring only asingle, powdered-iron core, broad-band, radio frequency transformer 33,instead of the plurality of transformers l9, 2i, and 22 in the Fig. 1circuit. It has the disadvantage, however, of requiring a 1 ohmtransmission line 36 which, as a practical matter, is somewhat diflicultof construction. In operation, however, the two circuits are obviouslythe full equivalent of each other.

Like Fig. 1, Fig. 2 also has its variant, shown in Fig. 2A, wherein thetransformer 33 is replaced by the auto transformer 33', the otherelements of the circuit remaining essentially unchanged. Likewise, as inFig. 1A, the leakage reactance of the transformer (either 33 or 33') maybe comworse on l pensated for by the insertion of a small variablecapacitor 3|a in series with the antenna and transformer primary whichneutralizes any small inductive component in the transformer.

In order to emphasize the advantages of the instant invention, therewill now be hypothesized two different circuits which do not meet therequirements of the instant invention, namely, step-down transformermeans, coupling to a plurality of channels including tunableseriesresonant circuits.

Consider first the hypothetical circuit of Fig. 3, which includes anantenna 4|, connected to a transmission line 42, to which are directlyconnected a plurality of multiplexed channels 43, 44, etc. The channel43, as an example, includes a series-resonant circuit 46, constituted ofan inductor 41 and a variable capacitor 48, connected in series acrossthe line 42. Since the resonance impedance of the circuit 46 is in theorder of 1 ohm, it is necessary to connect in series with this circuit aresistive impedance 5| of about 49 ohms value, so that the impedance ofthe antenna 4|, which is 50 ohms, may be substantially matched.

Consider, however, the effect of such an expedient upon the Q of thecircuit. wL, as shown hereinbefore, is approximately 200. The resistanceof the circuit, however, is now 1 ohm (circuit 46) plus 49 ohms (theresistor 5|) plus 50 ohms (the antenna 4|), a total of 100 ohms giving anet Q of approximately 2. This results in high energy loss and in lackof resolution, or unsharp tuning, for the channel 43. It is, therefore,evident that the hypothesized circuit of Fig. 3 lacks the high Q markingapplicants invention.

Next, hypothesize the circuit of Fig. 4, wherein an antenna 52 isconnected to a 50 ohm transmission line 53, across which are coupled themultiplex channels 54, 56, etc. The channel 54, for example, includes aparallel resonant circuit 51, comprised of a variable capacitor 58connected in parallel with an inductor 59. Energy is coupled to theinductor 59 by a coil 6| connected across the transmission line 53.-While the coupling between the coils BI and 59 constitutes atransformer in a sense, there is very great fiux leakage between thesecoils, because the coil 59 must present a relatively high inductivereactance in order to resonate with the capacitor 58. Unlike the instantinvention, the circuit 51 makes full use of the winding 59 to form theinductive component of the circuit.

The impedance reflected by the resonant circuit 51 into the transmissionline 53 is highest at the tuned resonance point rather than lowest, asit should be, this being characteristic of all parallel resonancecircuits. That is to say. off resonance, the impedance reflected intothe line 53 by the circuit 51 is relatively low, and hence considerableenergy will be drained from the line 53 without doing any good in thechannel 54. At resonance, when the channel 54 is tuned to accept theenergy, the impedance reflected into the line 53 will be maximum.

It is, therefore, evident that the hypothesized circuit of Fig. 4 hasthis disadvantage: the untuned channels tend to draw more energy fromthe line than does the channel which is tuned to the particularfrequency of the energy. Thus, much energy is wasted, and the system isrelatively low in efficiency.

From the above explanation, it will be seen that there has beendisclosed herein (embodied in several species) a multiplexed circuithaving simultaneously in combination the following advantages: it isbroad-band within the rrequency spectrum to which it may be tuned. Eachparticular channel has a very high Q, so that the energy loss isminimized. Each channel, when tuned to a particular frequency ofincoming energy, has a perfect impedanc match with the antenna or othertransmission means feeding the system, so that optimum transfer ofenergy at the frequency is achieved. Because the coupling impedance (the1 ohm secondaries) between any two circuits is so low compared to theuntuned impedance of each circuit itself, the feedback or cross-couplingbetween circuits is reduced to a minimum. In this way the localoscillators of the respective receiving circuits do not cross feedappreciably into the other circuits, thru the transmission line. All ofthe above features are attained without the use of vacuum tubes, withtheir consequent danger of overloading due to near-by transmitters.

As stated hereinbefore. although the particular examples haveillustrated receiving circuits employing fixed impedance antennas, it isobvious that, if desired, the teachings of the instant invention may beemployed equally well for transmitting circuits. Likewise, the antennasillustrated herein may be replaced by any suitable transmission linessuch as coaxial cables extending between receiving and transmittingstations.

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. It is, therefore, tobe understood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

What is claimed is:

1. A multiplex receiving circuit comprising a fixed impedance,broad-band antenna and a plurality of generally similar, multiplexedchannels connected in parallel to said antenna, each channel including abroad-band, step-down transformer having its high turns terminalsconnected to said antenna, a tunable, series-resonant circuit connectedacross the low turns terminals of said transformer, the impedance ofsaid circuit at resonance reflected thru its transformer beingsubstantially matched to said fixed impedance of said antenna and beingmuch higher 011' resonance; and a means for deriving a signal from oneof the elements of said circuit.

2. A multiplex receiving circuit comprising broad-band transmissionmeans; and a plurality 'of generally similar, multiplexed channelsconnected tosaid transmission means, each channel including abroad-band, step-down transformer having its high turns terminalsconnected to said transmission means, a tunable, series-resonant circuitconnected across .the low turns terminals of said transformer, theimpedance of said circuit at resonance reflected thru its transformerbeing substantially matched to the impedance of said transmission meansand being much higher 015 resonance, and a means for deriving a signalfrom one of the elements of said circuit.

3. A multiplex circuit comprising a fixed impedance, broad-band antenna;and a plurality of generally similar, multiplexed channels connected tosaid antenna, each channel including a broad-band, stepdown transformerhaving its high turns terminals connected to said antenna,

mum

a series-resonant circuit connected across the low turns terminals ofsaid transformer, the impedance of said circuit at resonance reflectedthru its transformer being substantially matched to said fixed impedanceof said antenna, and a signal amplifying means connected across aportion of said circuit.

4. A multiplex circuit comprising: broad-band transmission means; and aplurality of generally similar, multiplexed channels connected to saidtransmission means, each channel including a broad-band, step-downtransformer having its high turns terminals connected to saidtransmission means, a series-resonant circuit connected across the lowturns terminals of said transformer, the impedance of said circuit atresonance reflected thru its transformer being substantially matched tothe impedance of said transmission means and being much higher oilresonance, and a single amplifying means connected across a portion ofsaid circuit.

5. A multiplex circuit comprising a fixed impedance, broad-band antenna;a plurality of generally similar broad-band, step-down transformershaving their high turns terminals connected to said. antenna; and anequal plurality of generally similar, series-resonant circuitsconnected, respectively, across the low turns terminals of saidtransformers, the impedance of each said circuit at resonance reflectedthru its transformer being substantially matched to said fixed impedanceof said antenna and being much higher off resonance.

6. A multiplex circuit comprising broad-band transmission means; aplurality of generally similar, broad-band, step-down transformershaving their high turns terminals connected to said transmission means;and an equal plurality of generally similar, series-resonant circuitsconnected, respectively, across the low turns terminals of saidtransformers, the impedance of each said circuit at resonance reflectedthru its transformer being substantially matched to the impedance ofsaid transmission means and being much higher off resonance.

'7. A multiplex circuit comprising a fixed impedance, broad-bandantenna, a plurality of step-down broad-band transformers connected inparallel to said antenna, a plurality of tunable, series-resonantcircuits connected, respectively, to the low turns terminals of saidtransformers, and a plurality of signal amplifying means connected,respectively, one across a portion of each said circuit.

8. A multiplex receiving circuit comprising a fixed impedance,broad-band antenna; a stepdown, broad-band transformer having its highturns terminals connected to said antenna; a plurality of tunable,series-resonant circuits connected to the low turns terminals of saidtransformer, and a plurality of means for deriving signals from aportion of each said circuit.

9. A multiplex receiving circuit comprising broad-band transmissionmeans; a step-down, broad-band transformer having its high turnsterminals connected to said transmission means; a plurality of tunable,series-resonant circuits connected to the low turns terminals of saidtransformer, and a plurality of means for deriving signals from aportion of each said circuit.

10. A multiplex circuit comprising a fixed impedance, broad-bandantenna; a step-down, broad-band transformer having its high turnsterminals connected to said antenna; a plurality of series-resonantcircuits connected to the low I a i 10 turns terminals of saidtransformer, and a plurality of signal amplifying means connected,respectively, across a portion of each said circuit.

11. A multiplex circuit comprising broad-band transmission means; astep-down, broad-band transformer having its high turns terminalsconnected to said transmission means; a plurality of series-resonantcircuits connected to the low turns terminals of said transformer, and aplurality of signal amplifying means connected, re-

spectively, across a portion of each said circuit.

12. A multiplex circuit comprising a fixed impedance, broad-bandantenna; a step-down, broad-band transformer having its high turnsterminals connected to said antenna; and a plurality of series-resonantcircuits connected to the low turns terminals of said transformer.

13. A multiplex circuit comprising broad-band transmission means; astep-down, broad-band transformer having its high turns terminalsconnected to said transmission means; and a plurality of series-resonantcircuits connected to the low turns terminals of said transformer.

14. A multiplex receiving circuit comprising: a fixed impedance,broad-band antenna; stepdown, broad-band transformer means having thehigh turns terminals thereof connected to said antenna; a plurality ofgenerally similar multiplexed channels, each channel including atunable, series-resonant circuit connected to the low turns terminals ofsaid transformer means, the impedance of said circuit at resonancereflected thru said transformer means being substantially matched tosaid fixed impedance of said antenna and being much higher offresonance, and means for deriving a signal from a portion of saidcircuit.

15. A multiplex receiving circuit comprising: broad-band transmissionmeans; step-down, broad-band transformer means having the high turnsterminals thereof connected to said transmission means; a plurality ofgenerally similar multiplexed channels, each channel including atunable, series-resonant circuit connected to the low turns terminals ofsaid transformer means,

the impedance of said circuit at resonance refiected thru saidtransformer means bein substantially matched to the impedance of saidtransmission means and being much higher off resonance, and means forderiving a signal from a. portion of said circuit.

16. A multiplex circuit comprising: a fixed impedance, broad-bandantenna; step-down, broad- .band transformer means having the high turnsterminals thereof connected to said antenna; a

plurality of generally similar multiplexed channels, each channelincluding a series-resonant circuit connected to the low turns terminalsof said transformer means, the impedance of said circuit at resonancereflected thru said transformer means being substantially matched tosaid fixed impedance of said antenna and being much higher offresonance, and signal amplifying means connected across a portion ofsaid circuit. 1'7. A multiplex circuit comprising: broadbandtransmission means; step-down, broadband transformer means having thehigh turns terminals thereof connected to said transmission means; and aplurality of generally similar multiplexed channels, each channelincluding a, seriesresonant circuit connected to the low turns terminalsof said transformer, the impedance of said circuit at resonancereflected thru said transformer means being substantially matched to theimpedance of said transmission means and being much higher offresonance, and signal amplifying means connected across a portion ofsaid circuit.

18. A multiplex circuit comprising: a fixed impedance, broad-bandantenna; step-down, broadband transformer means having the high turnsterminals thereof connected to said antenna; and a plurality ofgenerally similar series-resonant circuits connected to the low turnsterminals of said transformer means, the impedance of each said circuitat resonance reflected thru said transformer means being substantiallymatched to said fixed impedance of said antenna and being much higher011 resonance.

19. A multiplex circuit comprising: broadband transmission means;step-down, broad-band transformer means having the high turns terminalsthereof connected to said transmission means; and a plurality ofgenerally similar seriesresonant circuits connected to the low turnster- REFERENCES CITED The following references are of record in the fileof this patent:

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